The invention relates broadly to the manufacture of t-butylstyrene (tBS) by oxidative dehydrogenation (OXD) of t-butylethylbenzene (tBEB) and in particular to the sharp separation of unreacted t-butylethylbenzene feed from t-butylstyrene product.
Tertiary-butylstyrene is a compound which has many uses; e.g., as a chemical intermediate, as a monomer or comonomer in the production of polymeric materials, and the like. Tertiary-butylstyrene has often replaced styrene in some applications because desirable physical and chemical product properties result from such a substitution. In addition, there are processes where styrene is not suitable but where tertiary-butylstyrene functions well.
Because tBS belongs to the same family as styrene, there are similarities in the chemistry of its preparation. One of the common properties is the tendency for the styrenics to polymerize whenever they are activated by chemicals or by heat. Some of the techniques used in purifying styrene can be used to purify tBS. However, because the boiling point of tBS is about 70.degree. C. higher than that of styrene, the tendency for tBS to polymerize is much greater than that of styrene in any of the commercial processes for purifying styrene.
Some of the differences between styrene and tBS derive from the compounds of the dialkenylbenzene family, which are present in tBS but not in styrene. These crosslinking compounds can polymerize to give a type of polymer that interferes with the operation of refining equipment. The crosslinked polymer has a tendency to collect in the equipment and to resist attempts to dissolve it.
Some of the other differences from styrene that arise in the separating of tBS into a pure product derive from the presence of the isomers of tBS and tBEB. Both the meta and para isomers are found in tBEB and tBS. The m-tBS has a boiling point that is intermediate between the boiling points of p-tBEB and p-tBS and is likely to be found in both the top and bottom products if a conventional distillation column were to be used for separating tBEB and tBS.
In copending application Ser. No. 646,266, filed Aug. 31, 1984, an extractive distillation process, has been disclosed for the separation of t-butylstyrene from an OXD reactor effluent containing tBEB and tBS using anhydrous sulfolane as solvent. This process works well; however, the use of reduced pressure and elevated temperature contribute considerably to the equipment, inhibitor, and utilities costs of the overall process.
Trials with anhydrous sulfolane as solvent in liquid/liquid extraction of OXD reactor effluent indicated that pure tBS could not be produced because anhydrous sulfolane and tBS are completely miscible.
It is, therefore, a principal object of the present invention to provide a separation process utilizing mild operating conditions to obtain a tBS product of acceptable purity from an OXD reactor effluent.